1. Field of the Invention
At present, crude oils and heavy oils are mainly used as fuel, but in accordance with the air pollution control legislation or regulations oils that contain sulfur as well as heavy metals in high concentrations cannot be used unless they are subjected to hydrodesulfurization, hydrodemetallization, exhaust gas desulfurization, or the like. Most of crude oils, though somewhat different depending on their sources, contain vanadium and nickel mainly in the form of porphyrin compounds. Usually the reaction conditions of hydrodesulfurization and hydrodemetallization are such that the reaction pressure ranges from 70 to 140 Kg/cm.sup.2 G and the reaction temperature ranges from 350.degree. C. to 450.degree. C. The vanadium and nickel in oils enter into reaction and accumulate in pores of catalysts. These catalysts are as large as about 0.5 cm to about 1.0 cm in length and about 1/32 inch to 1/16 inch in diameter. These catalysts usually are synthetic gel based catalysts and clays, that is, they are made by desorption of molybdenum, nickel and/or cobalt etc, from a solution or slurry of salts of these metals on a carrier such as silica, alumina; silica-aluminum or silica-magnesia etc. It is well known that as a result the catalytic activity is considerably lowered, and therefore it is no exaggeration to say that the life of catalyst is almost always determined by the amount of the accumulated vanadium, nickel, etc. For this reason the use of oils containing large amounts of metals is restricted. The metal content in crude oils largely differs depending on the oil-producing district, and it attains as high as 1,500 ppm in Venezuela crude oil. But, as, on the other hand, vanadium and nickel are valuable metallic raw materials, it is our present situation that we cannot overlook these highly metal-containing oils as the recovery source of valuable metals from the viewpoint of utilization of resources. In particular, vanadium is one of the most promising raw materials along with niobium in its high degree of utilization in future, and not only is it now in the limelight as the raw material of high tensile steel, the coating material of nuclear reactor, the super conduction material, etc., but also it is in wide use as the catalysts in various chemical industries as well as petroleum industry, the coloring agent for glass, the additive to titanium alloy, etc. Nickel is also in wide use as the raw material of special steels, stainless steels, etc. so that it is one of the valuable raw materials comparable to vanadium. Thus, in view of the limited production of these metals, it is of extreme importance that vanadium and nickel are recovered from these highly metal-containing oils for the purpose of utilizing resources.
Recently, in spent catalysts for desulfurization and demetallization which were used in the hydrogenation treatment of heavy oils that is in actual practice as one of the preventive methods for public nuisance such as air pollution, etc., the concentration of vanadium on spent catalyst is as high as 0.20-50% by weight, and the concentration of nickel is also as high as 0.10-15% by weight, so that it may be mentioned that these spent catalysts are high grade ores that are not found in nature.
2. Description of the Prior Art
As the process for selective removal of metals such as vanadium, nickel, molybdenum, etc. from spent catalysts there have been proposed several processes for selective extraction using ammonium sulfide (German Pat. No. 1,040,723) or glycolic acid, oxalic acid, etc. (U.S. Pat. Nos. 3,020,239 and 3,791,989) or an alkali (Japanese Application Disclosure No. 75,185/1975) and so on, and in addition to them, as the process for regeneration of catalysts in fluidized catalytic cracking deactivated by the accumulation of these metals there are known U.S. Pat. Nos. 3,122,510; 2,488,744; 3,147,209; 3,122,511; 2,481,253; and 3,234,145.
Also, as the process for recovering the above described valuable metals from spent catalysts there may be mentioned a process for extraction by an alkali (Japanese Application Disclosure Nos. 5,436/1977 and 11,995/1975), a process for extraction by ammonia (Japanese Application Disclosure No. 21,387/1972), etc.
All of these processes involve the technique of either removing vanadium or nickel after the spent catalysts have been subjected to oxidizing calcination so as to remove carbonaceous material, or regenerating the catalyst in high yield after the above described removal of vanadium and nickel. In these processes the vanadium, that is the object of the recovery, is converted to oxide (or oxides) on the catalyst by the oxidizing calcination, so that by chlorination, the greater part of it is converted to VOCl.sub.3 while very little VCl.sub.4 is formed. Moreover, in such a case, because of the comparatively large stability of the vanadium oxide the chlorination temperature should be higher than 600.degree. C. to recover almost all of vanadium accumulated on spent catalysts, but when the chlorination temperature exceeds 600.degree. C., the layer such as molybdenum and the carrier of the catalyst is also chlorinated and makes difficult the separation of metals for recovery.